Constructing Breaklines and Bathymetry DRAFT

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THIS PAGE IS CURRENTLY UNDER CONSTRUCTION

Tutorial Description

Constructing breaklines and bathymetry for modelling purposes requires judicious use of a range of potentially disparate data, and so there is a need to be careful and clean. This section describes the process of efficiently constructing bathymetry using a variety of data types and techniques. The goal of this exercise is to create a bathymetric surface that seamlessly integrates both high and low resolution data, tailored to the specific spatial needs of the model domain. The examples demonstrated here can be effectively applied to address data gaps in areas with limited data availability, such as small coastal estuaries. Notwithstanding this, it is important to note that studies often include a targeted and detailed data collection component, such as hydrographic surveys, resulting in a high resolution Digital Elevation Model (DEM) or Triangulated Irregular Network (TIN) production. In such cases not all the techniques presented below will be required.  

Skills described in this section include:

  • Creating breaklines.
  • Converting multiple elevation data types into scatter data.
  • Merging scatter sets.
  • Creating a seamless raster.

Model Domain

The tutorial focuses on Cudgen Creek, a small coastal estuary on the eastern Australian coastline. The model domain extends approximately 20 km north-south and 12km east-west to a depth of 50m.

M03 CC ModelDomain ahd 002.png

Requirements And Download

Requirement Brief Description
Data Download the Constructing Breaklines and Bathymetry Data Package MADDY TODO link data.
Assumed Knowledge It is recommended to complete the Meshing Module 3 (MADDY TODO update link) prior to completing this tutorial. If you run into any problems or need help, please contact support@tuflow.com

Prepare The Working Environment

Unzip the required Data Package to your preferred working location, for example E:\TUFLOWFV\Breaklines_Bathymetry.

  • The Completed_Module folder has the files for the completed tutorial.
  • The Module_Data folder has the files for the completed tutorial.
  • The Working folder is where files associated with mesh development will be saved.
Folder Structure.png

Note: All file paths referred to will be relative to this base directory. For example, Working\Dem\Lake_Coast_survey_AHD_MGA56.csv refers to E:\TUFLOWFV\Breaklines_Bathymetry\Working\Dem\Lake_Coast_survey_AHD_MGA56.csv.

Provided Project files

Module_Data\ Copy to Description
Base_Data.map Working\Map SMS map data file that will assist in the generation of DEM. The spatial reference system is GDA94 / MGA zone 56 (EPSG:28356).
Sample_creek_survey_AHD_MGA56.TXT Working\DEM A sample of point survey data. The spatial reference system is GDA94 / MGA zone 56 (EPSG:28356). The vertical datum is the Australian Height Datum (AHD).
Lake_Coast_survey_AHD_MGA56.csv Working\DEM Point survey data of the upstream lake and coastal zone. The spatial reference system is GDA94 / MGA zone 56 (EPSG:28356). The vertical datum is the Australian Height Datum (AHD).
Bathy_DEM_30m_AHD_MGA56.tif Working\DEM Combined offshore bathymetry and intertidal digital elevation model at a grid size of 30m.The spatial reference system is GDA94 / MGA zone 56 (EPSG:28356). The vertical datum is the Australian Height Datum (AHD).

Setup The SMS Project

Launch SMS and use the below steps and video to save the workspace in the Working folder:

1. From the menu bar select File > Save As.
2. Navigate to Working folder.
3. Save the workspace as Cudgen_Creek_001.sms.

Set the projection GDA 1994 MGA Zone 56 from the menu bar Display > Display Projection....

Use the below steps and video to set the workspace projection:

  1. Go to Display > Display Projection....
  2. Select Global projection.
  3. The Horizontal Projection dialog will appear. In the Filter strings: type GDA 1994 MGA Zone 56. Select the projection and OK > OK.

Use the below steps and video to open and set the display options for map files and aerial imagery:

1. Select File > Open.... Navigate to Working\Map\Base_Data.map and Open. Specify the display as below:
  • Within the Map Data panel turn on Breaklines to view the current display.
  • Select Display Options DisplayOptionToolSMS.png.
  • In the Display Options select the point/Node dropdown and set the the colour to red.
  • Check the Vertex attributes are on and update symbol attributes to a crosshair symbol +.
  • Select OK > OK.
2. Select File > Add Online Maps.... From the Get Online Maps dialog select World Imagery > OK. Specify the display as below:
  • From the project panel right click on World Imagery and select Transparency....
  • Update the transparency to 30%. Select OK.

Creating Breaklines

The examples provided in this section demonstrate techniques to build breaklines. Doing so is a core skill required to build bathymetric data sets for TUFLOW FV models, so investing time in learning this skill is worthwhile. In general, the goal is to digitise/construct breaklines as feature arcs in a map coverage that can then be both exported as a scatter set for geotiff creation and used directly within TUFLOW FV as 2d_zln breaklines at run time. Although some will be built via the steps below, the final breaklines for this model extent have been provided in the Map_Data and will be later used to build the model bathymetry.

Begin by opening the survey data as a scatter dataset. In this example the scatter data will serve as a visual aid for understanding the spatial distribution of the elevation values, which is essential for creating breaklines in a map coverage (see below). Use the below steps and video to import the survey data as a scatter set:

  1. Select File > Open.... Navigate to Working\DEM\Sample_creek_survey_AHD_MGA56.TXT and Open.
  2. The File Import Wizard dialog will appear. Specify the following:
    • Check that the File import option is set to Delimited.
    • Set the the Column delimiter to Tab and select Next >.
    • Select Finish.
    • Select OK for the warning: Specify the projection for imported data.
    • The data is in the same projection as the project window. Select OK.
  3. Within the Project panel right click on Sample_creek_survey_AHD_MGA56 > Zoom to Scatter.
  4. Select Display Options DisplayOptionToolSMS.png and specify the following Scatter options:
    • Under the Points check Use contour color scheme.
    • Check Scalar values.
    • Select the Scalar values font options and update to font size to 11.
  5. Use the Select Scatter Point tool to view the elevations at each point. This now provides a foundation for subsequent digitisation of spatially detailed breaklines as feature arcs in a map coverage

Since breaklines are created from feature arcs that can be snapped and interpolated to survey data, the survey data above must also be re-imported as a feature type within SMS. Follow the steps and video below to open the survey data as feature type data, which will enable us to construct the breaklines effectively:

  1. In the project panel right click on Map Data > New Folder. Rename it Breaklines.
  2. Again select File > Open.... Navigate to Working\DEM\Sample_creek_survey_AHD_MGA56.TXT and Open.
  3. The File Import Wizard dialog will appear. Specify the following:
    • Check that the File import option are set to Delimited.
    • The Column delimiter Tab should be checked. Select Next >.
    • From the SMS data type dropdown select Feature Data.
    • Select Create... and from the New Coverage dialog rename Area Property coverage Breaklines_gen.
    • Select OK > OK.
    • Select No when the the warning Arcs have not been mapped. Would you like to connect the points as one continuous arc? appears.
    • The data is in the same projection as the project window. Select OK.
    • Select OK for the warning: Specify the projection for imported data. As the data is in the same projection as the project window. Select OK.
  4. Using the Select Objects tool select the point within Breakline_gen and review the assigned elevations within the Z field. This data matches the scatter data set and will be used to interpolate elevations along breaklines.

With the survey data imported as a scatter (for depth guidance) and a coverage (for feature arc construction), breaklines are now able to be prepared.

The first breakline example involves interpolating the elevations along a feature arc between two survey points. Use the below steps and video as a guide:

  1. Zoom into the data (refer to video).
  2. Using the Create Feature Arc tool digitise an arc from elevation -2.30 to -2.32. Note snap the arc to each point (refer to the video). If snapping is not enabled refer to the Snapping Features section at Using Snapping in SMS.
  3. Using the Select Feature Arc tool select the new arc. Right click and select Redistribute Vertices.... Set the following attributes in the Redistribute Vertices:
    • From the drop down select Specified spacing.
    • Set an average spacing of 5. Select OK.
  4. Whilst the arc is still selected right click and select Smooth Arc(s).... Set the following attribute in the Smooth Arcs Tool dialog:
    • Set the Number of neighbors to 7.
    • Select OK.
  5. Again right click on the arc and select Interpolate Vertex Elevations.
  6. Using the Select Feature Vertex tool review how the elevation at each vertex (refer to the video).

The second example uses survey data points and user defined points to create two breaklines that represent a deep pond in the channel bathymetry. Use the below steps and videos as a guide:

First (outer) breakline

  1. Using the Create Feature Arc tool digitise an arc around the pond. Note snap the arc ends to lowest elevation points (-2.30) at the sides of the pond (refer to the video).
  2. Repeat step 1 for the other side of the pond (refer to video).
  3. Using the Select Feature Arc tool hold shift and select the both arcs. Right click and select Redistribute Vertices.... Set the following attributes in the Redistribute Vertices:
    • From the drop down select Specified spacing.
    • Set an average spacing of 5. Select OK.
  4. Whilst the arc is still selected right click and select Smooth Arc(s).... Set the following attribute in the Smooth Arcs Tool dialog:
    • Set the Number of neighbors to 7.
    • Select OK.
  5. Again right click on the arc and select Interpolate Vertex Elevations.
  6. Using the Select Feature Vertex tool review the elevation at the vertices (refer to the video).

Second (inner) breakline

  1. Using the Create Feature Point tool digitise a point within the feature arcs that were created in the previous steps (refer to the video).
  2. Update the elevation value of point in the Z field to -3.0.
  3. Using the Create Feature Arc tool digitise an arc as circle that starts and ends at the new feature point (refer to the video).
  4. Using the Select Feature Arc tool hold shift and select the both arcs. Right click and select Redistribute Vertices.... Set the following attributes in the Redistribute Vertices:
    • From the drop down select Specified spacing.
    • Set an average spacing of 5. Select OK.
  5. Whilst the arc is still selected right click and select Smooth Arc(s).... Set the following attribute in the Smooth Arcs Tool dialog:
    • Set the Number of neighbors to 7.
    • Select OK.
  6. Again right click on the arc and select Interpolate Vertex Elevations.
  7. Using the Select Feature Vertex tool review the elevation at the vertices (refer to the video).

The third example has the breakline elevation assigned to the feature arc. Use the below steps and video as a guide:

  1. Using the Create Feature Arc tool digitise an arc from the pond to the bridge. Note do not snap the arc to any point data in the coverage (refer to the video).
  2. Use the Select Feature Arc tool to select and update the elevation value to -2.5.
  3. Right click on the arc and select Redistribute Vertices.... Set the following attributes in the Redistribute Vertices:
    • From the drop down select Specified spacing.
    • Set an average spacing of 5. Select OK.
  4. Whilst the arc is still selected right click and select Smooth Arc(s).... Set the following attribute in the Smooth Arcs Tool dialog:
    • Set the Number of neighbors to 7.
    • Select OK.
  5. Again right click on the arc and select Interpolate Vertex Elevations.
  6. Using the Select Feature Vertex tool review the elevation at the vertices (refer to the video).

Once the map coverage has been prepared to create and assign elevations to the breaklines and associated vertices using the techniques above, it is then transformed into a scatter dataset. Use the below steps and video as a guide:

  1. Uncheck Sample_creek_survey_AHD_MGA56 Scatter Data.
  2. Right click on Breaklines_gen in the Map Data coverage. Select Convert > Map -> 2D Scatter.
  3. In the Map -> Scatter dialog set the Scatter Point Z-Value Source to Arc end points and vertex elevations. Leave the rest as the default and select OK.
  4. Uncheck Breaklines_gen map data.
  5. Use the Select Scatter Point tool to review the new Breaklines_gen Scatter Data.
  6. Right click on each scatter set and Remove.

Create Model Bathymetry

In real-world applications, the model bathymetry would typically go through several iterations to accurately represent the elevations throughout the model domain. However, for the purposes of this tutorial, a single iteration was undertaken to simplify the process. This section demonstrates how to consolidate multiple scatter datasets into a single bathymetric surface. Specifically, breaklines, point survey data and gridded data are all combined to create a single continuous elevation surface. When merging multiple datasets it is crucial to ensure that all inputs share the same projection. In this example the data is represented in Australian Height datum AHD and UTM Zone 56 of the Geocentric Datum of Australia (GDA94) within Map Grid of Australia (MGA).

Use the below steps and videos to convert breaklines into a scatter set:

  1. Right click on Breaklines from the Base_data folder.
  2. Select Convert > Map -> 2D Scatter.
  3. In the Map -> Scatter dialog set the Scatter Point Z-Value Source to Arc end points and vertex elevations.
  4. Rename it Breaklines.
  5. Leave the rest as the default and select OK.
  6. Select Display Options and uncheck Scalar values.

A .csv is provided containing point survey data that covers the lake, canal and coastal regions. Use the below steps and videos to load the .csv as a scatter data:

  1. Select File > Open.... Navigate to Working\DEM\Lake_Coast_survey_AHD_MGA56.csv and Open.
  2. The File Import Wizard dialog will appear. Specify the following:
    • Check that the File import option are set to Delimited.
    • Set the the Column delimiter to Comma and select Next >.
    • Select Finish.
    • Select OK on the warning Specify the projection for imported data.
    • The data is in the same projection as the project window. Select OK.
  3. Within the Project panel right click on Lake_Coast_survey_AHD_MGA56 > Zoom to Scatter and review data.

A combined offshore bathymetry and intertidal DEM at a grid size of 30m has been provided has been provided as a .tif file. Use the below steps and video to open and convert the gridded data into scatter data.

  1. Select File > Open.... Navigate to Working\DEM\Bathy_DEM_30m_AHD_MGA56.tif and Open.
  2. Right click on Bathy_DEM_30m_AHD_MGA56.tif and select Convert To > 2D Scatter. Accept the default name and select OK. Note it might take some time to convert the data to a scatter.
  3. Once complete remove Bathy_DEM_30m_AHD_MGA56.tif from GIS Data.
  4. Zoom into the newly created scatter data and use the Select Scatter Point to review the elevations.

Using the below steps and video to merge the scatter datasets:

  1. From the SMS tool bar select Scatter > Merge Sets.
  2. Under Select scatter sets to merge check all.
  3. Name the new scatter Bathy_001 and select OK.
  4. Select OK if the error the Numerical limitation encountered arises and close the merge report. For information on the Scatter merge report refer to SMS Scatter .
  5. Right click and Remove Breaklines, Lake_Coast_survey_AHD_MGA56 and Bathy_DEM_30m_AHD_MGA56 from the Scatter Data panel. Now review the newly created scatter dataset Bathy_001.

Now that the elevation datasets are in a single scatter (Bathy_001) it can be converted into a gridded raster. Use the below steps and video to convert the merged scatter data into a raster:

  1. Select Bathy_001 scatter set and right click. Select Convert > Scatter -> Raster.
  2. In the Interpolate to Raster dialog set the Cell size to 5.0 and select OK.
  3. Save the new raster into Working\DEM\ and keep the default name Bathy_001.tif. Note it might take some time to convert the data to a raster.

To remove unnecessary data and reduce the file size trim the new raster using the below steps and video:

  1. Select Bathy_001.tif and right click. Select Convert To > Trimmed Raster.
  2. From the Coverage with polygons: drop down select Map Data/Base_data/Bathy_trim.
  3. Set the Output raster: path relative to Working\DEM\ call it Cudgen_Creek_bathy_001. Select OK.
  4. When the Trim Raster processing window is complete select OK. Note it might take some time for the trimmed raster to load into the SMS workspace.
  5. Right click and Remove Bathy_001.tif from the GIS Data panel.

By default the SMS Trim Raster tool produces a Tag Image File grid (.tif). As TUFLOW FV typically uses an ASCII grid (.asc) or binary grid (.flt) formats to assign bathymetry or topography the Cudgen_Creek_bathy_001.tif is exported as an .asc. Use the below steps and video to export the raster:

  1. Select Cudgen_Creek_001.tif and right click. Select Export.
  2. In the export window update the cell size to 5.0 and select OK.
  3. From the Save as type drop down select Arc Info ASCII Grid Files (*.asc) name the raster Cudgen_Creek_bathy_001.asc.
  4. Right click and Remove all raster files and scatter data from the project panel.

Feedback

If you have any queries, feedback or requests for new functionality you would like added to the tutorial modules, please feel free to get in contact with support@tuflow.com.

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Conclusion And Next Steps

Well done on generating breaklines and using multiple elevation data types to build bathymetric surface in SMS Community.

Return to the Tutorial Introduction Page to complete further meshing and model build tutorials.

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